Medical devices are implanted in humans or animals for many reasons. Some of these devices are used to monitor one or more bodily functions. Other devices are used to stimulate or out rightly control bodily functions. Often, the medical devices will include some kind of communications circuit for receiving signals used to power and/or control the devices, or for sending outside a patient's body information about the medical device or bodily functions monitored or controlled by the device. Typically, medical devices are powered by an electric power supply, such as a battery, that provides the voltage and current needed for their operation.
Medical devices are often intended to be implanted in a patient's body for many years, and in some instances, for the rest of a patient's life. As such, the power supplies used to power these long-term medical devices are implanted in a patient at a location that permits easy access from outside the patient's body for recharging or replacement of the power supply. Typically, these power supplies are recharged by energy drawn from an alternating magnetic field transmitted from outside of a patient's body to inside of the patient's body using a pair of coils. The pair of coils includes a first coil that is part of a transmitter that generates the alternating magnetic field and a second coil that is part of a receiver that is also implanted in a patient's body. Alternatively, the second coil implanted in a patient's body may be connected directly to a power supply or a medical device implanted in the patient. Because the second coil is often implanted subcutaneously in a patient to permit easy access to it from outside of the patient's body, there is a risk that the second coil, over time, may become intermittently inoperable, or even completely fail, because movements of the patient over time cause the secondary coil to break. Thus, it would be desirable to provide a coil that can be implanted in a patient at a location that is easily accessible and that would reliably operate over time, notwithstanding bending of the coil caused by a patient's movements over time.